Device for cooling and thermal conditioning of a tubular object

ABSTRACT

A device ( 1 ) for cooling and/or thermal conditioning of hot preforms or parisons ( 6 ), in particular of parisons for the production of blow-moulded bottles made of plastic material, limits and/or reduces the deformations of said parisons during cooling by containing the transverse deformations of the end close to the opening ( 8 ) of the parison. The device is provided with a tubular portion of prolongation which wraps totally around the parison that rests on its internal surface with one of its sections ( 9 ). Described herein is the corresponding method for cooling the parison ( 6 ).

FIELD OF THE INVENTION

The present invention relates to a device and a method for thermalconditioning of moulded objects, and in particular thermal conditioningof tubular objects such as parisons for the production of plasticbottles by blow-moulding, reducing the deformations of the parisons upontheir extraction from the injection mould.

PRIOR ART

In the production of blow-moulded bottles or containers made of plasticmaterials, for example bottles or jars made of PET for foodstuffs,beverages, mineral water, fruit juices, preserves, and the like, oneprocess of fabrication is that of injection-moulding of the parisons,from which may be obtained, in a subsequent operation ofstretch-blow-moulding, the finished container with even a considerablelapse of time between the production of the parison and the operation ofblowing; i.e., after the injection-moulding operation, the parisons arecooled and stored, or else taken to the blow-moulding, plant, which islocated in a different production site.

Cooling of the parisons can be obtained by extracting them from theinjection mould when they are still hot and relatively plastic, but inany case of a consistency such that they may be gripped and transferredinto special containers with circulation of coolant, known as coolingbeakers or tubes or moulds, where the cooling operation is completed.

With the aim of increasing the rate of output of injection-mouldingpresses, one trend is that of extracting the parison from the injectionmould at the highest temperature possible, but this increases all thecritical aspects of manipulation of the parison on account of itsconsiderable plasticity and susceptibility to getting damaged duringtransfer to the cooling devices outside the press.

Another trend is that of cooling the parison as fast as possible, bothto obtain a higher productivity, and so that the plastic material of theparison will be as amorphous as possible.

In addition, according to some state-of-the-art production systems, theparison is extracted from the injection mould using various devices formechanical gripping, for example mechanical grippers, and transferred asfast as possible into the cooling beaker. If the temperature ofextraction is excessively high, and the parison excessively plasticized,the latter is deformed also by the mechanical accelerations and by theimpact during handling. Consequently, a problem that can arise duringthis second cooling step is that the parison, on account of thermalcontraction or mechanical stresses, is deformed, assuming a bent shape,even with a few millimeters of misalignment between the two ends of theparison.

This can lead to various types of problems; for example, numerousrejects during the subsequent operation of heating of the parison priorto the operation of blowing. The parison is pre-heated in an infraredfurnace, the lamps or heating surfaces of which pass very dose to theparison, and owing to the excessive deformations of the latter, bangagainst it, or else heat it in an uneven way, so bringing about furtherdeformations. In addition, the shape tolerances are a parameteraccording to which the quality and the reliability—and hence theprofit—of a possible external subsupplier of parisons, and in general ofany production process, whether internal or external, are measured. Afurther disadvantage that may occur is that a deformed parison, afterthe operation of stretching with as special bar gives rise, in thebottom, region of the stretched solid, to non-uniform wall thicknesses,which in the subsequent operation of blow-moulding of the bottle leadsto bursts.

One method according to a current technique for preventing geometricalerrors is that of inserting into the parison, which is in turn insertedinto the cooling beaker, a force plug, plunger or mandrel for preventingbends from occurring, which, however, leads to the need for anadditional plug-carrying plate and the movement of an additionalmechanical member in the cycle time of the machine.

Other solutions have been devised for prolonging the cooling of theparison in the injection mould without delaying too much the output rateof the injection-moulding press.

A problem that the present invention seeks to solve is that of reducingor eliminating the deformations that a parison may undergo duringcooling for thermal conditioning, or that it may have undergone beforecooling for thermal conditioning after the injection-moulding operationis completed, with a high repeatability of the production process.

Another purpose that the present invention seeks to achieve is tosimplify the state-of-the-art devices for eliminating the aforesaiddeformations, for example without recourse to the use of containmentplugs inside the parison in the cooling beaker.

The above purposes are achieved by a device having the characteristicsaccording to Claim 1, and with a method having the characteristicsaccording to Claim 16.

Advantages that are obtained by means of the present invention, inaddition to the solution of the problems described above and to theimplementational simplicity of the invention, are the fact of enablingextraction of the parison from the injection mould at a highertemperature with limited deformations on the cooled parison. Inaddition, cooling beakers according to the present invention can bereplaced on already existing plants for cooling or thermal conditioningand blow-moulding, without having to make other modifications to theplant, at extremely contained costs and during a customary extraordinarymaintenance operation by staff that may even be not particularly highlyqualified. Some particular embodiments of the invention presented in thedependent claims regard, devices for extraction of the parison from thecooling device and/or thermal-conditioning device.

LIST OF FIGURES

Further advantages that may be achieved with the present invention willbecome apparent, to the person skilled in the sector, from the followingdetailed description of two non-limiting examples of particularembodiments, with reference to the attached figures, of which:

FIG. 1 is a schematic side view of the internal body of a device, orcooling beaker, for cooling and/or thermal conditioning of a tubularobject, according to one first embodiment of the present invention;

FIG. 1A is a schematic sectional view according to the plane A—A of theinternal body of FIG. 1;

FIG. 1B is a schematic three-dimensional view of the internal body ofFIG. 1;

FIG. 2 is a schematic sectional view of two assembled devices, accordingto the embodiment of FIG. 1;

FIG. 2A is a schematic side view of a first example of parison;

FIG. 2B is a schematic side view of a second example of parison;

FIG. 3 is a schematic three-dimensional view of mechanical means forextracting the parisons from a plurality of cooling beakers according toa particular embodiment of the present invention;

FIG. 3A is a detailed schematic view of the assembly made up ofmechanical means for extraction and cooling beakers represented in FIG.3;

FIG. 4 is a schematic side view of a second embodiment of a deviceaccording to the present invention;

FIG. 4A is a schematic sectional view according to the plane B—B of thedevice of FIG. 4; and

FIG. 4B is a schematic three-dimensional view of the external sleeve ofthe device of FIG. 4.

DETAILED DESCRIPTION

FIGS. 1, 1A, 2, and 2A are schematic representations of one detail andof the ensemble of a first preferred embodiment of a device for thetransport, cooling and/or thermal conditioning of tubular objects 6, inparticular, parisons, according to the present invention. In whatfollows, the said device is as a whole designated by the referencenumber 1, and alternatively also referred to as “cooling beaker”.

Cooling beakers of this sort, which in themselves are well known to thecurrent art, are used for example to complete cooling of the parisons,outside the injection mould with which they were produced, so as to beable to increase the output rate of the press. The parisons areextracted from the injection mould when they are still relatively hotand in a state in which they are more plastic and deformable than atroom temperature, but of a consistency such that they can be gripped,handled and moved. The beaker in FIGS. 2, 2A comprises an internal body2 on which is inserted externally a sleeve 3 made, like the body 2, of amaterial that is a good thermal conductor and preferably light, such asaluminium. In the external surface of the internal body 2 there are madehelical grooves 4 which, being closed by the sleeve 3, form channels fora coolant, for example water or some other appropriate fluid.

On its front side, the beaker 1 has an open front end 5 designed toenable introduction of a parison 6—or at least of its elongated portion10—which is to be cooled or thermally conditioned, into an internalcavity 7 made in the internal body 2. The parison 6 of FIG. 2A comprisesa portion in the proximity of the open end 8 on which there can be made,for example, the thread of the screw top of the future blow-mouldedbottle, an annular projection for tearing seals and for fixing tear tabsof the aforesaid bottle top, and a second annular projection 9, alsoreferred to in what follows as “ring”, which typically also has thepurpose of making possible gripping and movement of the blow-mouldedbottle in the processing stations set downstream or in the user'splants. Frequently, but not necessarily for the purposes of the presentinvention, the ring is also the maximum radial projection of the regionof the neck of the bottle (or anyway of the region close to the open end8). In general, the threaded region and that of the ring on the parison6 already, have the same dimensions that they will have on theblow-moulded bottle, whilst the elongated portion 10 and the rounded andclosed end 11 of the parison 6 are sized in such a way that they can bedilated by blow-moulding and, possibly, by biaxial stretching so as toassume the dimensions of the finished is bottle or container. Since thepresent invention is particularly advantageous with parisons ofelongated shape, in what follows the term “axial direction” or“longitudinal direction” shall mean the direction parallel to the largerdimension of the parison, and by “radial direction”, “transversedirection” or “lateral direction” is meant the direction perpendicularto the larger dimension and to the axis of the parison or tubular object6. From the state of the art there is already known a wide range ofsystems for bestowing on the elongated portion 10, which is initiallyinserted very hot and easily deformable into the cooling beaker, a shapewith acceptable tolerances; for example, it is possible simply to leavea maximum play between the wall of the hot portion 10 to be expanded andthe wall of the internal cavity 7 of the internal body, for instance ofa few tenths of millimeter in the case of a parison that isapproximately 150 mm long. Obviously, this play will be reduced to zeroin the contact regions between the parison 6 and the walls of theinternal cavity 7; i.e., the gap between the parison and the walls ofthe internal cavity 7 varies locally from region to region of theparison 6. This fact limits the axial bending of the portion 10 that isto undergo expansion.

The modalities of contact or otherwise of the rounded end 11 of theparison with the bottom 12 of the internal cavity 7 of the internalbody, according to the known art, are numerous: for example, the end 11of the hot parison can be brought into contact with the bottom 12, orelse inserted at a distance and possibly brought into contact with thebottom 12, by deforming it in various ways or by sucking the entireparison towards the bottom 12.

According to certain solutions of the known art, the threaded end of theinserted parison 6 is allowed to project out of the beaker 1, inparticular when the parison 6 is introduced into the cooling beaker 1,bringing to bear upon it the ring 9 or other radial projection of theparison. In this case, particularly with parisons like the one in FIG.2A, with a part 13 close to the open end 8 having a tapered crosssection which is narrower than the remainder 14 of the bulb, if theparison 6 is not, for example, constrained by a plug inserted inside it,the open end 8,13, if cooled too fast, frequently bends considerably,since the narrower part 13 cannot be contained by the walls of theinternal cavity 7, and faulty parisons may be produced, with accentuatedelbow-like bends in the vicinity of the open end 8. The applicant hasencountered parisons of approximately 150 mm in length with errors oflinearity of even 2–3 mm or more between the ends of the parison.

Other deformations of the parison can result from the operations ofextraction from the injection mould and of transfer from this to thecooling beakers, all the more in that the current aim is to bringforward extraction and abbreviate the time for cooling the parison inthe mould. In certain cases the parison can thus prove excessivelyplastic, whilst the accelerations, decelerations and impact duringextraction, for example with mechanical grippers or the like, andmovement towards the cooling beakers 1, can also lead to deformationsthat are unacceptable for the customer or for the subsequent productionsteps.

According to the present invention, the cooling beaker or device 1 ischaracterized in that it comprises containment means 15, represented inFIG. 1, designed to contain and/or reduce by contact the radialdisplacements of the open end 8 due to deformations of the parison 6, ofthermal origin or deriving from the previous handling operations. In thepreferred embodiment, represented in FIGS. 1, 1A, 2, the containingmeans 15 basically consist of a tubular portion with through lateralslits, so as to obtain a pair of prolongations on the front part 5 ofthe internal body 2, preferably in a position which is symmetrical withrespect to a meridian plane of the beaker 1, the said slits extending inthe longitudinal direction of the beaker. Without departing from thescope of the present invention, the front prolongations which providethe containing means 15 can even be just one, which embraces the openend of the parison 6 with a sufficient angle of envelopment, or elsethey may number more than two. This is obtained by producing anappropriate number of through slits on the wall of the tubular portion.

The two prolongations 15 are shaped so as to define, on the inside ofthe beaker, supporting side surfaces 16, against which the open end 8 ofthe parison 6 can rest laterally, i.e., in the radial direction,following upon its deformation. In the example of FIG. 2A, eachprolongation 15 defines a sector of substantially cylindrical surface,against which the annular edge of the collar or ring 9 (i.e., the partof the open end 8 of the parison that presents the maximum radialprojection), or some other chosen region of the parison, comes to rest,undergoing deformation on account of thermal shrinkage.

The shape of the internal cavity 7 and of the lateral supportingsurfaces 16, or else both of these, are defined, starting from thegeometry of the parison 6 in such a way as to adapt them to one another.

The supporting surface or surfaces 16 are shaped and sized in such a waythat, between the surface or surfaces and the section for supporting theparison, chosen for contact, is set at least one minimum radial gap, oralso a maximum radial interference, of a pre-set value. The said minimumradial gap, or maximum interference, can be calculated with reference tothe dimensions of a parison 6 of nominal dimensions and geometry or,equivalently, of a parison 6 at the temperature of extraction from theinjection mould, for example a few tenths of millimeters of radial gapbetween the edge of the ring and the corresponding cylindrical surfaceof contact 16 made on the prolongations 15. In this case, advantageouslya parison 6 can be inserted, by bringing its bottom 11 to bear upon thebottom 12 of the cavity 7, and, thanks to the cylindrical surface orsurfaces 16, the ring 9 will be contained laterally, but is free toslide longitudinally owing to the thermal contraction caused by cooling.

Alternatively, the contact surface or surfaces 16 may be sectors of aflared surface or may have the shape of a truncated cone which openstowards the outside of the beaker 1, in order to allow also for thethermal reduction of the diameter, for example, of the ring 9 or otherregion of contact on the open end 8.

The devices as defined above make it possible, once inserted into theinternal cavity 7, to straighten a parison 6 which is already deformedby heat as a result of a previous automatic manipulation, for example totransport it from the injection mould to the cooling beaker.

The surface above the cylindrical surface 16 (FIG. 2) advantageously—forexample depending upon the ratio between the diameter of the elongatedpart of the parison and the external diameter of the ring—may form anample flaring that opens outwards so as to constitute a lead-in for theparisons that are inserted into the cavity 7.

Advantageously, for example by aspirating the air inside the internalcavity 7 through the channel 18 open on the bottom 12 of the cavity,there is produced a negative pressure for increasing the rate of heatexchange between the parison 6 and the cooled internal body 2,notwithstanding the gap existing in some regions between the parison andthe walls of the internal cavity 7. Initially, when the material of theparison 6 is still considerably plastic, the negative pressure deformsalso the walls of the elongated portion 10, causing them to adhere tothe walls of the internal cavity 7.

FIGS. 3 and 3A are schematic representations of a further aspect of thepreferred embodiment of FIG. 1. In accordance with the prior art, rowsof a number of cooling beakers 1 are fixed on a plate or other support,which can be moved, for example, by a rotating arm. The reference number18 designates as a whole the mechanical means for extracting theparisons from the internal cavities 7 of the beakers.

The mechanical means 18 comprise a number of extraction bars 19 thatmove in a longitudinal direction with respect to the beakers 1 and areactuated by a system of levers and hydraulic cylinders. Each extractionbar 19 comprises a plurality of holes or cutaway regions 20, throughwhich the cross section of one or more beakers 1 can pass. Present onthe edges of the cutaway sections 20 are two teeth 21, or some othersimilar type of radial projections, which are prolonged inside thebeakers 1 through the longitudinal slits 22 that separate the twolongitudinal prolongations 15 from one another and which, when the bars19 are in the lowered position, are inserted under a region where thereis a radial expansion of the cross section of the end 8 of a parison,for example under the ring 9. When a hydraulic cylinder is actuated, thecorresponding extraction bar 19 is raised, translating parallel toitself along the axis of the beakers 1. The pairs of teeth 21 sliding inthe slits 22 bear upon the rings 9, or other regions of radial expansionof the sections 8 of the parsons, and extract a row of parisons 6 fromthe corresponding beakers 1. The radial projections 21 may also havedifferent shapes, even ones not resembling teeth, provided that they arecapable of extracting the parisons 6 from the beakers 1.

FIGS. 4, 4A and 4B relate to a second preferred embodiment of thepresent invention, in which the tubular portion that forms a pair ofprolongations 15 is obtained as a prolongation of the external sleeve 3instead of the internal body 2. The criteria of sizing the internalcavity 7 of the internal body 2, and the determination of the gaps andof the play between the portion 10 of the parison that is to undergoexpansion and the open end 8, and between the walls of the cavity 7 andthe supporting surfaces 16 are similar to the preferred embodimentdescribed previously. This second embodiment is simpler to produce, andcan be mounted on a pre-existing internal body not provided withprolongations 15. In addition, a “change of format” can be obtained in asimpler way, in the sense that, by changing the external sleeve 3, aninternal body 2 can house, for example, both a parison 6 for bottleswith standardized rings having an external diameter of 28 mm, of thetype illustrated in FIG. 2A, and a parison with a ring having astandardized external diameter of 38 mm, of the type illustrated in FIG.2B.

Without departing from the scope of the present invention, the devicesdescribed above may undergo numerous modifications. For example, inaddition to undergoing modifications that are within the reach of aperson skilled in the sector, the said devices can find application inthe thermal conditioning of parisons for containers or moulded objectsmade of materials other than polyethylene terephthalate, such as HDPE,PP, and PE.

1. A device for post-mold cooling and/or thermal conditioning of a hottubular object, outside the injection mold with which the tubular objectwas produced, provided with a first closed end and a second open endwith a ring projecting radially from the cylindrical surface of thetubular object in the proximity of the second open end and constitutingthe maximum radial projection of the tubular object, wherein the devicecomprises: a tubular internal cavity provided with an open end for theintroduction of said tubular object, shaped to accommodate a firstportion of said tubular object set in the proximity of the first closedend and to control the deformations thereof; a tubular element isextended coaxial from the tubular internal cavity and the tubularelement is shaped to accommodate a second portion of said tubular objectin the vicinity of said second open end; an internal supporting surfaceof the tubular element is shaped to contain and/or control, by means ofcontact on the ring the deformations that are produced, in a directiontransverse to the axis, during cooling and/or thermal conditioning ofsaid tubular object; and the internal supporting surface has a dimensionsuch that, at the temperature of insertion of the hot tubular objectinto the internal cavity, there is set at least one minimum radial gapor a pre-set maximum radial interference.
 2. The device according toclaim 1, in which the tubular element is provided with at least onethrough longitudinal slit that forms a discontinuity in the internalsupporting surface.
 3. The device according to claim 1, in which thetubular internal cavity contains and constrains, at least partially,thermal deformations of the first portion of the tubular object, and isof diameter such as to produce, with the wall of the tubular object, agap of a size not greater than a pre-set maximum amount after cooling.4. The device according to claim 2, in which it comprises an internalbody and a coaxial external sleeve fitted on the internal body.
 5. Thedevice according to claim 4, in which said tubular element constitutesan axial prolongation of the internal body.
 6. The device according toclaim 4, in which said tubular element constitutes an axial prolongationof the external sleeve.
 7. The device according to claim 2, in which theinternal supporting surface is substantially cylindrical.
 8. The deviceaccording to claim 2, in which the internal supporting surfacesubstantially has the shape of a truncated cone, and widens towards theopen end of the device.
 9. The device according to claim 2, in whichmechanical means are provided for extraction of the tubular object fromthe tubular internal cavity.
 10. The device according to claim 9, inwhich the mechanical means of extraction comprise a plate provided witha hole of diameter greater than the diameter of the tubular element andprovided with at least one radial tooth designed to slide along saidlongitudinal slit for pushing the tubular object in the longitudinaldirection.
 11. A cooling tower for tubular objects wherein it comprisesa plurality of cooling devices in accordance with claim
 1. 12. Thecooling tower according to claim 11, wherein there are providedmechanical extraction means comprising one or more extraction bars forextracting simultaneously a plurality of tubular objects from acorresponding plurality of said cooling devices.